Localized heating for defect isolation during die operation

ABSTRACT

According to an example embodiment, a method for testing a semiconductor die is provided. The semiconductor die has circuitry on one side and silicon on an opposite side, and the opposite side may be AR coated. The opposite side is thinned, the die is powered, and a portion of the circuitry is heated to cause a reaction (e.g., a circuit failure or recovery) in a target region. The circuitry is monitored, and the circuit that reacts to the heat is detected and analyzed.

FIELD OF THE INVENTION

The present device relates generally to semiconductor devices and theirfabrication and, more particularly, to semiconductor devices and theirmanufacture involving defect isolation.

BACKGROUND OF THE INVENTION

The electronics industry continues to rely upon advances insemiconductor technology, including integrated circuits, to realizehigher-functioning devices in more compact areas. For many applications,realizing higher-functioning devices requires integrating a large numberof electronic devices into a single silicon wafer. In addition, many ofthe individual devices within the wafer are being manufactured withsmaller physical dimensions. As the number of electronic devices pergiven area of the silicon wafer increases, and as the size of theindividual devices decreases, testing processes become more importantand more difficult.

Many defects in integrated circuits can recover or fail at highertemperatures. For instance, circuit sites exhibiting temperaturesensitive defects, such as charge trapping and ionic contamination, canrecover when heated. Traditionally, isolation of defective sites hasbeen attempted by heating the entire device during extensive electricaltesting. Such electrical testing, however, does not always work.Moreover, even if a unique node is electrically identified, the physicaldefective site usually cannot be identified.

Semiconductor technology would benefit from a practical method andapparatus for heat testing integrated circuits for isolation ofdefective sites.

SUMMARY OF THE INVENTION

The present invention is exemplified in a number of implementations andapplications, some of which are summarized below. According to anexample embodiment, the present invention is directed to a method fortesting a semiconductor die. The semiconductor die has circuitry on oneside and silicon on an opposite side. The opposite side is thinned. Thedie is powered via a power supply, and heat is directed via the oppositeside to a portion of the circuitry. The circuitry is monitored, and acircuit that reacts to the heat is detected therein.

According to another example embodiment, the present invention isdirected to a system for testing a semiconductor die. The die hascircuitry on one side and silicon on an opposite side. The systemincludes a first means for thinning the opposite side, a second meansfor directing heat via the opposite side to a portion of the circuitry,and a third means for monitoring the circuitry and detecting therein acircuit that reacts to the heat. The first and second means areoptionally implemented using the same tool, e.g., a laser.

According to yet another example embodiment, the present invention isdirected toward a system for testing a semiconductor die havingcircuitry on one side and silicon on an opposite side, wherein theopposite side is AR coated. The system includes a milling machine forthinning the opposite side, a laser arrangement for directing heat viathe opposite side to a portion of the circuitry, and a microscope formonitoring the circuitry and detecting therein a circuit that reacts tothe heat.

The above summary of the present invention is not intended to describeeach illustrated embodiment or every implementation of the presentinvention. The figures and detailed description which follow moreparticularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 shows a system for testing a semiconductor device, according toan example embodiment of the present invention;

FIG. 2 shows another system for testing a semiconductor device,according to another example embodiment of the present invention;

FIG. 3 shows another system for testing a semiconductor device,according to another example embodiment of the present invention;

FIG. 4 shows another system for testing a semiconductor device,according to yet another example embodiment of the present invention;and

FIG. 5 shows another system for testing a semiconductor device,according to still another example embodiment of the present invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

The present invention is believed to be applicable to a variety ofdifferent types of semiconductor devices, and the invention has beenfound to be particularly suited for devices requiring or benefiting fromanalysis of temperature-sensitive defects. While the present inventionis not necessarily limited to such devices, various aspects of theinvention may be appreciated through a discussion of examples using thiscontext.

FIG. 1 illustrates a first example embodiment in which a system 100 fortesting a semiconductor die 120 that has a circuit side 140 and a backside 150, with the back side 150 thinned to no more than about 100microns. A first heat source 110 is used to direct heat 160 at a portionof the backside 150 of the semiconductor die 120. The semiconductor die120 is powered, and a circuit monitor 130 is coupled to thesemiconductor die 120 for monitoring the circuitry and for detectingtherein a circuit that reacts to the heat.

For instance, heat source 110 may include a laser, such as anear-infrared laser having a wavelength of about 1-2.5 microns. A lasersuch as 321IR (1064 nm Nd: YAG) available from Zeiss, Inc. may bemodified to provide sufficient power in this regard. The Zeiss 321 IR isa near IR scanning microscope; using this type of device, the monitor130 is implemented along with the heat source 110 as part of one unit.

FIG. 2 illustrates another example embodiment, in which a system 200 isadapted for testing a semiconductor die 120. Similar to the system shownin FIG. 1, the system 200 further includes a second heat source 210 thatis used to conventionally heat the semiconductor die 120 prior toheating with the first heat source 110. Heat source 210 may include, forinstance, devices using heating methods such as convection, conductionor radiation, or a combination thereof. Such devices may include itemssuch as a peltier device, heat tape, and heat elements.

An example method for testing a semiconductor die, according to anotheraspect of the present invention, is directed to a semiconductor die thathas circuitry on one side and silicon on an opposite side, wherein theopposite side is coated with anti-reflective material (“AR” coated”) tominimize the reflected light when laser-heating. First, the oppositeside is thinned. The die is then powered via a power supply, and heat isdirected via the opposite side to a portion of the circuitry. Thecircuitry is monitored, and a circuit in the semiconductor die thatreacts to the heat is monitored for specific reactions such asintermittent opens/shorts in conductors and between conductors due to,for example, expansions in the metal or surrounding materials.

Thinning the semiconductor die may be accomplished in various manners,and to various degrees. For instance, the device may be thinned usingconventional processes such as FIB (focused-ion beam) milling, lapping,polishing, laser-chemical etching, and using tools such as Chip UnZip®,available from Hyper Vision, Inc. In an example implementation, thesemiconductor die is thinned to less than about 100 microns. In anotherexample implementation, a target area of the semiconductor die isfurther thinned by locally thinning to about 8 microns. It has beendiscovered that the transmission of laser power improves as morematerial is removed from the die. As the transmission of power improves,less power is necessary to achieve desired results. In oneimplementation, a laser having a wavelength of between about 400 and 600nanometers is used to locally thin the die.

Heating the semiconductor die may be accomplished, for example, with alaser beam having a wavelength of about 1-2.5 microns focused on aportion of the circuitry within the semiconductor die. It has beendiscovered that temperature increases of about 50° C.-200° C. areachievable with about 100-200 MW of power focused on areas in diameterof about 1-5 microns. It has further been discovered that heating with alaser having a wavelength of about 1.3 microns produces improved heatingover lasers having other wavelengths. The portion of the circuitryfocused upon may include, for instance, a specific node within thecircuitry. Heat from the laser beam may, for example, be absorbed by aportion of the circuitry that reacts. In one implementation, thereaction to the heat includes a circuit that recovers from a failure. Inanother implementation, the reaction to the heat includes a circuit thatfails. In another implementation, the reactions can be due to causing ashort and causing an open; each of these can be considered a circuitfailure or circuit recovery, depending upon the application.

Monitoring the circuit may include monitoring parameters such as voltageshifts, Iddq shifts, and Pattern Pass/Fail.

In another example embodiment, heating the semiconductor die furtherincludes conventionally heating the die, using methods such asconvection, conduction, and radiation, prior to heating with a laserbeam. For instance, the die can be conventionally heated to atemperature just below the threshold for detecting a reaction therein. Aportion of the circuitry may then be heated with a laser beam, therebycausing that portion of the circuitry to exceed the temperaturethreshold necessary to cause a reaction.

FIGS. 3 and 4 show a system for isolating a defect within the circuitryin a semiconductor die 320 having a circuit side 340 and a backside 350,wherein the backside 350 is AR coated, according to another exampleembodiment of the present invention. In one example application, thebackside 350 of the semiconductor die 320 is thinned to no more thanabout 100 microns. A laser 310 is used to direct a beam 360 at thebackside 350 of the semiconductor die 320. The laser 310 may be includedas part of a near-infrared laser scanning confocal microscope, such asthe Zeiss 321IR. A circuit monitor 330 is coupled to monitor the circuitwithin the die. An objective 370 is placed between the laser 310 and thedie 320. Initially, the objective is used to expand the beam. A circuitthat reacts to the laser beam is detected by the circuit monitor 330.The objective 370 is then changed to objective 470, and the laser beamis re-focused as a smaller beam 480. The circuit monitor 330 againdetects a circuit that reacts. This process can be repeated, therebymore narrowly-isolating the defect.

According to another example embodiment, a defect can be isolated usinga laser having a spot mode. Yet another example embodiment includesusing a raster scan. These embodiments may be used in conjunction withother methods for isolating defects described herein. For instance,after the general area within a semiconductor die in which a defectexists has (or defects have) been located, a “spot” mode, vector mode ora raster scan mode may be used to further isolate the defect(s) withinthe general area.

FIG. 5 shows a system for isolating a defect within circuitry in asemiconductor die 520 having a circuit side 540 and a backside 550,according to another example embodiment of the present invention. Thebackside 550 of the semiconductor die 520 is locally thinned as shown tono more than about 8 microns. A laser or a FIB etcher, 510 is used todirect a beam 560 at the locally thinned area of the semiconductor die520. A circuit monitor 530 is coupled to the semiconductor die 520 formonitoring anode 562 in the circuitry (564) and detecting therein acircuit that reacts. The laser 510 can include a high-powered visiblelaser, such as an Argon Ion Laser emitting in the visible spectrum(e.g., 488 um and 515 nmd). The beam 560 heats the circuitry within thesemiconductor die 520, the heat at the surface propagates into the die,and the circuit monitor 530 detects a circuit therein that reacts.

In one embodiment, the laser 510 is for both laser-etching for localthinning and also for local-heating.

While the present invention has been described with reference to severalparticular example embodiments, those skilled in the art will recognizethat many changes may be made thereto without departing from the spiritand scope of the present invention, which is set forth in the followingclaims.

What is claimed is:
 1. A method for testing a semiconductor die havingcircuitry on one side and silicon on an opposite side, the methodcomprising: thinning the opposite side; while operating the die,directing heat, via the thinned opposite side, toward a portion of thecircuitry; and monitoring signal outputs from the circuitry anddetecting therefrom a circuit that reacts to the heat.
 2. A method fortesting a semiconductor device, according to claim 1, wherein thinningincludes at least one of: lapping, laser-chemical etching, andpolishing.
 3. A method for testing a semiconductor device, according toclaim 1, wherein thinning includes reducing the thickness of the siliconto less than about 100 microns.
 4. A method for testing a semiconductordevice, according to claim 1, wherein thinning includes locally reducingthe thickness of the silicon to less than about 8 microns.
 5. A methodfor testing, according to claim 4, wherein locally reducing includesusing a visible laser-generating light, having a wave length in a rangebetween 400 and 600 nm, and therewith heating the silicon.
 6. A methodfor testing a semiconductor device, according to claim 1, whereindirecting heat includes focusing a laser beam at portions of thecircuitry.
 7. A method for testing a semiconductor device, according toclaim 6, wherein focusing the laser beam at portions of the circuitryincludes raster scanning.
 8. A method for testing a semiconductordevice, according to claim 7, wherein heat from the laser beam isabsorbed by the circuit that reacts to the heat.
 9. A method for testinga semiconductor device, according to claim 7, wherein focusing the laserbeam includes applying about 100-200 mW of laser power focused at about1-5 micron diameter spots.
 10. A method for testing a semiconductordevice, according to claim 7, wherein the laser beam is directed towarda target node in the circuit.
 11. A method for testing a semiconductordevice, according to claim 7, wherein the laser beam is focused on asmaller area in response to detecting a reaction in the device.
 12. Amethod for testing a semiconductor device, according to claim 11,wherein the laser beam is re-focused in a smaller area in response todetecting a reaction in the device.
 13. A method for testing asemiconductor device, according to claim 6, wherein focusing the laserbeam at portions of the circuitry includes using a spot mode.
 14. Amethod for testing a semiconductor device, according to claim 7, whereinthe laser beam wavelength is between about 1 micron to 2.5 microns. 15.A method for testing a semiconductor device, according to claim 1,wherein the circuit recovers from a failure.
 16. A method for testing asemiconductor device, according to claim 1, wherein the circuit fails.17. A method for testing a semiconductor device, according to claim 1,further comprising heating at least a portion of the semiconductordevice.
 18. A method for testing a semiconductor device, according toclaim 17, wherein heating occurs before the step of directing heat. 19.A method for testing a semiconductor die, according to claim 18, whereinthe operation of the die does not include providing power to the dieusing a constant-current source.
 20. A method for testing asemiconductor device, according to claim 17, wherein heating includesheating by at least one of: radiation, convection or conduction.
 21. Amethod for testing a semiconductor device, according to claim 17,wherein heating includes heating the die to a temperature just below thethreshold temperature needed to cause a predetermined reaction.
 22. Amethod for testing a semiconductor die, according to claim 21, whereinthe operation of the die does not include providing power to the dieusing a constant-current source.
 23. A method for testing asemiconductor die, according to claim 1, wherein the signal outputsinclude at least one of: voltage shifts, Iddq shifts and patternpass/fail criteria.
 24. A method for testing a semiconductor die,according to claim 23, wherein the operation of the die does not includeproviding power to the die using a constant-current source.
 25. A methodfor testing a semiconductor die, according to claim 1, wherein theoperation of the die does not include providing power to the die using aconstant-current source.